Table of Contents
Biology in the News
How the Body Senses a Range of Hot Temperatures
Chapter 17
The Cell Cycle Creates New Cells
Replication, Transcription, and Translation: An Overview
Cell Reproduction: One Cell Becomes Two
How Cell Reproduction is regulated
Environmental Factors Influence Cell Differentiation
Cloning an Organism Requires an Undifferentiated Cell
Therapeutic Cloning: Tissues and Organs
Triplet Code
Chapter 18
Tumors can be Benign or Cancerous
Cancerous Cells Lose Control of their Functions and
Structures
How Cancer Develops
Advances in Diagnosis Enable Early Detection
Cancer Treatments
The 10 Most Common Cancers
Most Cancers can be prevented
Chapter 19
Your Genotype is the Genetic Basis of your Phenotype
Genetic Inheritance Follows Certain Patterns
Other Dominance Patterns
Other Factors Influence Inheritance Patterns and Phenotype
Sex-linked Inheritance: X and Y Chromosomes Carry Different
Genes
Chromosomes May be Altered in Number or Structure
Many Inherited Genetic Disorders Involve Recessive Alleles
Chapter 20
DNA Sequencing Reveals Structure of DNA
DNA can be cloned in the Laboratory
Genetic Engineering Creates Transgenic Organisms
Gene Therapy: The Hope of the Future?
Biology in the News
In Science Daily, I read an
article titled How the Body Senses a Range of Hot Temperatures. Over the past two decades researchers
have been studying how the human body senses many different temperatures. Until recently the research has shown that
proteins on the surface of nerve cells let the body feel a range of
temperatures from extremely hot to warm.
Now research is showing that there are only a few proteins, called ion
channels that distinguish many different temperatures. All the research was recently published in
the Journal of Biological Chemistry.
Research
shows that ion channels are located in pores in the cell membrane. The ion channels can turn sensors on or off by
choosing if charged ions can go through the channels. New information shows when the temperature
sensors combine they create heteromeric channels that can sense temperature
between what the original channels can detect.
One heteromeric channel I thought was very interesting was the
TRPV3. This channel responds to
temperatures of approximately 85 degrees (Fahrenheit) and can sense flavors
such as cinnamon, vanilla, oregano, and rosemary. When the TRPV3 combines with another channel
called TRPV1 the result is temperature response is at 92 degrees. The study also showed that heteromeric
channels had a higher sensitivity than the original channels that created
it. It is interesting that the sensors
that sense heat also sense flavors too.
Researchers hope that in the future this information can possibly treat
temperature sensitivity disorders.
Chapter 17
The Cell Cycle Creates New Cells
Replication, Transcription, and Translation: An Overview
Human DNA is made up of 46 chromosomes (23 exact
pairs). DNA replication is the process
of coping DNA before cell division. A
gene is segment of DNA that contains a code or recipe.
(http://en.wikipedia.org/wiki/Gene,
accessed 20 Feb 2012)
A gene is the smallest functional unit of DNA and every unit
produces a specific outcome. One arm and
leg of a chromosome is called a chromatid and the other arm and leg of the
chromosome is called a sister chromatid.
The process of replication is unzipping and uncoiling DNA
strands. Each strand serves as a
template for the creation of a new DNA strand.
DNA nucleotides are linked and positioned by DNA polymerase moving
nucleotides into their place. Nothing
is left to chance, precise base pairing guarantees an exact copy is made. A centromere holds duplicate daughter (sister
chromatids) chromosomes together. Some
mistakes are made in the DNA code occurring most often during DNA
replication. Some mistakes happen due to
drugs, in vitro toxins, or viruses.
Sometimes there is no effect to cell mutations and other times cell
mutations can result in cell death or cancer.
Repair enzymes try to repair mutations and some are fixed.
Transcription is the process of copying DNA of a gene and
turning it into mRNA (messenger ribonucleic acid). It is the process of converting a gene code
to RNA form. DNA within the region of a gene starts to
unwind. RNA polymerase assists in
copying the base sequence in the RNA nucleotides. The primary transcript is made including
introns and exons. Introns are edited by
enzymes to get rid of any sections that don’t carry genetic information. The parts of the introns that don’t serve a
purpose dissolve back into raw cell material.
Exons carry sequences of genetic information that is linked correctly and
end up with messenger RNA strand. It is
a message that is in template form that is translated into a specific sequence
of amino acids. This message is in an
encrypted code know as a triple code. It is called triple code because it has three
bases of mRNA called codons. In a DNA
molecule the nucleus in each cell contains so much information. This information remains inside the cell but
the information in them can be copied and carried out of the cell by RNA. The information in the cell is the genetic
code (sequence of nucleotide bases). The
genetic code is written in 3 (base) letter words and every three base word
gives instructions to one amino acid.
The words are arranged in certain way so amino acids build into
polypeptides which then mature into a protein.
There are 64 different codons (3 letter words) but only 20 different
amino acids. Many different codons
encode each amino acid except for the start codon methionine (AUG). All genes in RNA begin with the start codon
methionine (AUG). Even though there is
only one way to start a codon there is three ways to stop (UAA), (UAG), and
(UGA).
Translation occurs in the cytoplasm ribosomes and takes the
recipe converting the mRNA into one or more proteins. So to recap mRNA (messenger) is basically a
copy of the “recipe” and tRNA (transfer) are small RNA molecules that are in
many different shapes and then escorts amino acids to the ribosome (site of
translation). Ribosomes are made out of
ribosomal RNA (rRNA) and protein. Ribosomes
have the enzymes that catalyze the peptide bond formation. They also contain the sites for mRNA and
incoming amino acid tRNA. The process
starts with initiation where the start codon AUG and initiator codon carry tRNA
and form a complex. Next is elongation
where tRNA brings specific amino acids to already developing proteins. The elongation happens when each amino acid
is added to the chain. Last, any of the
stop codons UAA, UAG, or UGA are used to terminate the developing chain and the
protein is released from the ribosome.
A Cell
Reproduction: One Cell Becomes Two
Pounds of cells are replaced daily. Of all these cells there are two types of
cell reproduction on humans. One is the
mitotic cell cycle where new diploid cells are generated and contain
chromosomes in pairs. The other
generates haploid gametes that contain chromosomes not in pairs called meiotic
cell division.
There are two different periods that occur within the cell
cycle. The mitotic cell cycle lasts for
approximately 18-24 hours. There is a
sequence of cell growth phases in order: interphase, prophase, metaphase,
anaphase, telophase, and cytokinesis phase.
Interphase
(http://biology.about.com/od/mitosis/ig/Mitosis-Image-Gallery/,
accessed 20Feb 2012)
Interphase is the cycle
that longest has growth period.
Interphase is divided into three categories 1. G1 phase 2 .S phase 3. G2
phase 4. G0. During the cell cycle the
G1 phase is very active and is the primary growth phase. During the S phase DNA is synthesized for
cell division. The final growth phase
before cell division is G2. Lastly in G0
the cells go through a non-growing, non-dividing state.
Prophase
(http://biology.about.com/od/mitosis/ig/Mitosis-Image-Gallery/,
accessed 20 Feb 2012)
In prophase protein
structure called the mitotic spindle is formed. The nuclear membrane dissolves and metabolic
activity decreases so the concentration goes to dividing.
Metaphase
In metaphase duplicate chromosomes form a single line at the
equator between the centriole poles.
During anaphase duplicate chromosomes separate by popping apart from
each other.
Telophase
Telophase is when everything returns to normal. Then in cytokinesis a contractile ring of
protein filaments form at the middle of the cell and tighten forming a cleavage
furrow. Two daughter cells are formed as
the contractile ring pinches them apart.
Then during the mitotic phase the nucleus and cytoplasm divide during
approximately one hour of the cell cycle.
Mitosis (nuclear division) is followed by cytoplasmic division which is
cytokinesis. With the process of
cytokinesis daughter cells are formed.
Daughter cells are identical to the parent cells and this cycle repeats
over and over. During mitosis duplicated
DNA is distributed. Then between the two
daughter nuclei the nucleus divides.
Meiotic is the process of two nuclear divisions where the
chromosomal material is rearranged and reduced by half during the formation of
sperm and eggs. Daughter cells are
haploid because meiosis reduces the chromosome number by half. Meiotic cell division includes two effective
division processes called meiosis l and meiosis ll. Meiotic cell division have
four stages: prophase, metaphase, anaphase, and telophase. In meiosis l the cell goes through S phase
where the DNA and all 46 chromosomes are duplicated. During prophase the duplicated chromosomes
pair up and swap gene sections called crossing over. This then creates a combination of both the person’s
parent’s chromosomes. During the rest of meiosis l pairs of chromosomes are
separated from each other rather than the duplicates of each pair. In meiosis ll the chromosomes are not
duplicated again. During meiosis ll the
23 duplicated chromosomes line up and the sister chromatids are separated from
each other. When gene sections swap in
meiosis l none of the four haploid daughter cells are exactly alike. That is why if two people have more than one
child each child has some similarities but do not look the same.
How Cell Reproduction is regulated
Not all cells divide at the same rate as other cells. Some cells stop dividing after adolescence
where other cells divide throughout our lives. A certain protein called cyclic
controls the progression of G1, S, and G2 phases through fluctuations in cyclic
concentrations. Cyclic activate certain
proteins that start specific events within the cell like DNA replication or the
formation of the mitotic spindle. There
are check points at the end of phase G1 and G2 to make sure everything has been
completed properly. Lastly if certain
nutrients aren’t available the cell can stop if needed. Cells also regulate tissue growth and organ
size.
(http://www.biologycorner.com/bio1/cellcycle.html,
accessed 23 Feb 2012)
Environmental Factors Influence Cell Differentiation
Every cell in our bodies came from a single cell. Every cell in our bodies has the same genetic
code within it. Why don’t cells all look
the same? Through a process called
differentiation cells become different than the original parent cell. Some cells become skin (epithelial cells),
organs, bone and blood to give some examples.
At different stages in our lives cells differentiate expressing
different genes. It is very evident in
the beginning of life. When cells get
past the eight cell stage the environment that surrounds the cells becomes
different than the environment of the cells surface. During later stages in our lives
differentiation is effected by the local environment and the developmental
history of cells.
Cloning an Organism Requires an Undifferentiated Cell
There are two different techniques for reproductive cloning
called embryo splitting and somatic cell nuclear transfer. In embryo splitting an egg is fertilized in
vitro (test tube) and allowed to divide to the eight-cell stage. At this stage all eight cells can be divided
and if placed into women could develop into spring for herd improvement. In somatic cell nuclear transfer involves
creating a clone of an adult organism. Somatic
cells have a full set of DNA instructions.
This technique was used in 1997 when scientist cloned a sheep named
Dolly. The clone of Dolly didn’t live
very long making scientists question if the adult cells are already damaged. The process involves scientists combing a
somatic cell from an adult with a fertilized egg that has had the nucleus
removed. The nucleus from the adult
somatic cell already contains the instructions for making a copy to clone the
adult animal. The egg is then inserted
into a segregate mother enabling it to develop.
The baby will be an exact clone of the adult that it was cloned from.
Dolly the Sheep
Therapeutic Cloning: Tissues and Organs
Therapeutic cloning is defined as a procedure in which
damaged tissues or organs are repaired or replaced with genetically identical
cells that originate from undifferentiated stem cells. (http://medical-dictionary.thefreedictionary.com/therapeutic+cloning,
accessed 16 Feb 2012) The goal is to be able to take a single cell from one patient
and create new tissue or even a new organ for another patient. This is a way to create new cells without
having the risk of tissue rejection. Although
this treatment is a little ways off when it becomes available it will be
beneficial to many people.
Triplet Code
Chapter 18 Cancer
1 in 3 people will
experience cancer in their lifetimes.
1 in 4 people will die from cancer.
Tumors can be Benign or Cancerous
There are two characteristics of normal cells. Normal cells remain in one location for their
lifetime (except for blood cells).
Normal cells have regulatory mechanisms to keep the rate of cell
division in check. Hyperplasia is when
cells increase their division and in some cells hyperplasia is not normal. These out of control cells then form a mass
of cells called a tumor. Not all tumors
are cancers. If tumors stay in one place
the mass of cells are called benign tumors.
These cells still have the same structure as the cells they divided
from. Sometimes benign tumors can turn
into something more damaging.
(http://en.wikipedia.org/wiki/Malignant_tumor,
accessed 23 Feb 2012)
Cancerous Cells Lose Control of their Functions and
Structures
If cells advance to becoming cancer, the cell structure
changes. Abnormal structural changes of
a cell are called dysplasia. Dysplasia
is often a sign that tumor cells are precancerous. The tumor becomes more and more disorganized
while cells continue to pile up on each other randomly. A tumor isn’t defined as cancer until at
least some cells lose all aspects of organization, structure, or regulatory
control. Tumors that remain in one place
are called in situ cancer and can usually be surgically removed if it is caught
early. If the cancer goes through
additional changes then metastasis can result.
Metastasis is the spread of cancer to another organ or place in the
body. This happens when cancer cells
break away from the main tumor and get into the blood stream or lymph. Cancers that metastasize and travel through
blood or lymph then invade normal tissue resulting in malignant tumors. Malignant tumors often grow out of control
overrunning tissues and organs.
How Cancer Develops
For cancer to develop two things have to happen at the same
time. One is the cell has to
uncontrollable grow and divide ignoring the signals to stop dividing. The other is that when cells genes become
abnormal and stop functioning correctly the cell goes through physical changes
making the cell break away from other cells.
Tumor suppressor genes and pronto-oncogenes normally regulate genes that
promote cell growth and division. When
pronto-oncogenes mutate or become damaged, cancer called oncogenes can occur by
increasing internal cell growth and division faster than usual. Another regulating gene that is supposed to
stop all unchecked cell growth is the tumor suppressor gene. When this gene becomes damaged it contributes
to cancer because cell activities continue to be unrestricted. The gene p53 has the primary role to inhibit
cell division of cells that already have cancerous features. When this gene becomes damaged many different
cancers can develop. The last class of
gene that contributes to cancer is mutator genes. These genes are supposed to be involved in
DNA repair during the copying process.
When this gene mutates errors are prone to DNA replication causing
mutations in other genes at a fast rate.
The transformation process of a normal cell turning into a
cancerous cell is called carcinogenesis.
A carcinogen is any substance or physical factor that causes
cancer. Some viruses and bacteria also
contribute to some cancers. Viruses that
contribute to cancer are human papillomavirus, hepatitis B and C, HIV,
Epstein-Barr virus, and human T-cell leukemia.
Only 15% of viruses and bacteria account for cancer. Other things that lead to cancer is
environmental chemicals, tobacco, radiation, a person’s diet, and internal
factors.
Advances in Diagnosis Enable Early Detection
Early detection of cancer is important in surviving
cancer. X rays can view tumor masses but
isn’t the most effective imaging available.
Other advanced imaging techniques are also used. PET otherwise known as positron-emission
tomography create a 3D image showing metabolic activity in the body. Another imaging technique is magnetic
resonance imaging (MRI) that uses short bursts of a powerful magnetic field to
show cross sections of the body. An MRI
can see tumors hidden by bone and between tissues. Some of these genes have already been
identified. This is very controversial
because some diseases have no cure.
Would someone want to know that they had the genetic components to
possibly develop a disease without a cure?
Instead of doing genetic testing maybe another test would be better
accepted. There is an enzyme that isn’t
usually found in normal cells but is usually found in cancerous cells. If people were tested for this enzyme cancer
could be detected early helping the survival rate.
Cancer Treatments
Cancer is treatable.
There are many variables but with the current treatments available 50%
of all cancers are cured. The current
treatments consist of surgery, radiation, and chemotherapy. Surgery removes tumor masses. Radiation focuses on a specific area to kill
cancer cells. Chemotherapy puts
cytotoxin (cell damaging) chemicals in the body to destroy cancer cells. Some chemo drugs stop cells from dividing and
others interfere with DNA replication.
Drugs designed to stop cell division the effects are nausea, hair loss,
anemia, and have a hard time fighting infections. There are many treatments being developed and
are currently in a trial phase. Vaccines
are being created to prevent certain cancers as well. Cancer requires lots of energy because they
are dividing so rapidly. Researchers are
excited about anti-angiogentic drugs that restrict blood vessel growth. These drugs may be able to “starve” tumors by
limiting their blood/nurturance supply.
The 10 Most Common Cancers
The top ten cancers are skin, lung, breast, prostate,
colon/rectum, lymphoma, urinary bladder, kidney, uterus, and leukemia.
There are three main types of skin cancers with melanoma
being the deadliest. When looking at
dark patches of your skin you should evaluate them using the “ABCD” rule. A: asymmetry meaning the two halves don’t
match; B: border meaning to check if there is an irregular shape; C: color
watching differences in color or if it is black; D: diameter means to measure
and make sure the size is less than a pea.
Other warning signs might be scaliness, itching, oozing, and
bleeding. The other two main skin
cancers are basal and squamous cell cancers having a 95% cure rate.
Skin Cancer
(http://www.medicinenet.com/script/main/art.asp?articlekey=107539,
accessed 21 Feb 2012)
Lung cancer in most cases is preventable. Smoking is the biggest culprit to lung
cancer. As of now there isn’t screening
to detect this cancer early. Most of the
time it is discovered when the cancer is already advanced. This cancers cure rate isn’t very good with
the one year survival rate at 41% and 15% over five years.
Lung Cancer
(http://images.search.yahoo.com/search/images?_adv_prop=image&fr=yfp-t-435-17&va=picture+of+lung+cancer,
accessed 21 Feb 2012)
Breast cancer is most common in women but can also occur in
men. Breast cancer is found by self-exams,
doctor exams, and mammograms.
Researchers say that age plays a large part in this cancer and the risk
increases as someone ages. There are
other risk factors like early menstruation and hormone replacement therapy that
can increase someone’s risk for breast cancer.
Breast Cancer
(http://www.encyclopedia.com/topic/breast_cancer.aspx,
accessed 21 Feb 2012)
Men are affected by prostate cancer and the biggest risk is
advancing age. Prostate cancer is
generally discovered early with digital rectal exam or by a prostate- specific
antigen test. The survival rate for
prostate cancer is up from 25 years ago from 69% to 99%.
Prostate Cancer
(http://www.medicinenet.com/prostate_cancer_pictures_slideshow/article.htm,
accessed 21 Feb 2012)
Colon and rectum cancers start in the form of polyps. These polyps are small benign growths that
develop within the colon lining. Most
polyps never become cancerous and if they do become cancerous it takes many
years. The American Cancer Society recommends
a colonoscopy every ten years after the age of 50.
Lymphoma is cancer of lymphoid tissues including Hodgkin’s
disease and non-Hodgkin’s lymphoma.
Researchers feel the risk factors for this cancer have to do with a
person’s immune system. Treatments
usually involve radiation and chemotherapy.
Urinary bladder
cancer is treatable with surgery if found early. Risks of urinary bladder cancer are smoking,
living in urban areas, and jobs that expose someone to rubber, leather, and
dyes. Blood in the urine is an important
sign to get checked by a doctor. If
caught early the survival rate is between 73-97%. If the cancer has spread the survival rate
drops to only 6%.
The risks of kidney cancer are smoking, heredity, gene
mutations, exposure to toxic agents, and age.
The main treatment is to remove the cancerous kidney if the other kidney
is in good working condition. If
removing a kidney isn’t an option then radiation and chemotherapy are
used. (Chemotherapy doesn’t usually have
any effect)
Papillary Renal
(kidney) Carcinoma (cancer)
(http://www.robertsreview.com/cancer_pictures_kidney.html,
accessed 22 Feb 2012)
Uterine cancer includes cancers of the cervix and endometrium.
The main symptom is abnormal bleeding.
Cervical cancer is usually caused by a virus called the human
papillomavirus. A new vaccine is almost
100% effective in blocking strains of this cancer causing virus. There is a range of risk factors but once again
smoking was on top. The survival rates
are high for these cancers with appropriate treatment.
(http://images.search.yahoo.com/search/images,
accessed 22 Feb 2012)
Leukemia is cancer of immature white blood cells in bone
marrow. In advanced stages bone marrow
becomes completely filled with cancerous cells.
The cause for leukemia is still unknown but scientists have some
ideas. This cancer affects both adults
and children. The treatment for leukemia
is chemotherapy and is then usually followed by a bone morrow transplant. The chance of survival has increased over the
past few years especially in children.
Most Cancers can be prevented
Most cancers can be prevented. At least 60% of cancer cases are believed to
be caused by smoking and having a poor diet.
Reducing sun exposure greatly reduces the occurrence of skin
cancer. Overall eating a diet high in
fruits and veggies, exercising, practicing healthy habits, and avoiding the sun
reduce the risk of cancer. Other things
we can do to is to get regular cancer screenings. We need to be conscious of changes in our
skin and any lumps in breast or tentacles.
Knowing your family history allows you to know any genetic defects. Even though cancer is a scary word we need to
be informed about cancer in general. With
diet and exercise the risks of cancer are lowered and above all DO NOT SMOKE!!
(http://images.search.yahoo.com/search/images?_adv_prop=image&fr=yfp-t-435-17&sz=all&va=fruits+vegetables,
accessed 22 Feb 2012)
Chapter 19
Your genotype is the genetic basis of your Phenotype
Humans have 23 pairs of chromosomes which account for 22
pairs of autosomes and 1 pair of sex chromosomes. An autosome is defined as a chromosome that
is not a sex chromosome (http://www.answers.com/topic/autosome,
accessed 24 Feb 2012). Even when
autosomes appear identical there can still be slight differences between the
pair. The un-identical produced genes
are called alleles. Because alleles are
different they code for different proteins and have a slightly different
structure than the original gene.
Sometimes someone will have an identical pair of alleles in their genes
called homozygous. A person with two
different alleles of a gene is called heterozygous.
Scientists believe alleles are the result of millions of
years of mutation. These mutations and
all the various genes in humans are summed up as the human gene pool. The uniqueness of each person is due to
different alleles in approximately 22,000 genes. An individual’s set of alleles is called a
genotype. This is better defined as, the
combination of alleles located on homologous chromosome that determines a
specific characteristic or trait (http://www.answers.com/topic/genotype,
accessed 24 Feb 2012). A phenotype is the expression of a trait due to genetic
and environmental influences. This has a great effect on the
person’s characteristics called phenotype.
Types of different phenotype traits are a person’s hair color, eye
color, skin color, body type, and abilities.
Phenotypes that aren’t physical traits aren’t recognized as easy. Things like a person’s blood type and
susceptibilities to disease have to be tested for. A
person’s genetics account for many health factors but not all of them. The lifestyle someone chooses to live also
plays a big part in the person’s life.
Genetic Inheritance Follows Certain Patterns
Alleles are assigned uppercase and lowercase letters to help
researchers document them. People who
have the same two alleles of a gene are homozygous and people with different
alleles are heterozygous. A punnett
square is a square used in genetics to calculate the
frequencies of the different genotypes and phenotypes among the offspring of a
cross (http://www.merriam-webster.com/dictionary/punnett%20square, accessed 24 Feb 2012).
This is a simple way to show all the
patterns of possible inherited alleles in a particular genotype. Gregor Mendel was an educated monk from the
1800’s. Through the use of plants he
figured out genetics and how traits are passed from parents to their
children. One experiment Mendel
preformed was to see if breeding a yellow pea plant with a green pea plant
produced yellow or green peas. He found
they only produced yellow peas but when two pea plants with a recessive green
gene were bred that the plants produced mostly yellow peas but some green peas
(75/25).
Gamets are haploid with half the number of
chromosomes and genes of each parent. In
the law of segregation the allele that a parent contributes to a gamet is done
randomly. A heterozygous parent has a
50% chance of donating a specific allele to each gamet. One neat example is a person’s hairline. A person’s hairline is controlled by a single
gene with two alleles. One allele
controls if someone has a widow’s peak and the other controls a straight
hairline. This is a major reason why
variation exists in people and also a reason why traits
can skip a generation. Dominant is
defined as designating an allele that does not produce a
characteristic effect when present with a dominant allele or relating to a
trait that is expressed only when the determining allele is present in the
homozygous condition (http://www.thefreedictionary.com/recessive, accessed 25 Feb
2012). Dominant is then defined as an allele of a gene pair that masks the effect of the other when both are present in the
same cell or
organism (http://www.definitions.net/definition/Dominant, accessed
25 Feb 2012). Most recessive alleles
don’t have an advantage or disadvantage to the homozygous recessive
person. The alleles that effect
appearance stay in the gene pool because they don’t harm anyone. On the other hand alleles that are harmful in
the human population are kept in check by homozygous recessives dying out
early, where harmful alleles in a heterozygous population survive. Dominant alleles don’t mean a specific trait
is guaranteed. In fact I learned some
dominant traits are actually very rare even though they are dominant. How a dominant allele works has to do with
the combination of recessive and dominant heterozygotes. With the use of a punnett square a person can
map the probability of certain traits.
Other Dominance Patterns
One of Gregor Mendel's great discoveries was the Principle
of Dominance and part of his discovery was incomplete dominance. Gregor
Mendel (July 20, 1822 – January 6, 1884) was an Austrian monk whose
studies of the inheritance of traits in pea plants helped to lay the foundation
for the later development of the field of genetics (http://www.newworldencyclopedia.org/entry/Gregor_Mendel,
accessed 6 March 2012).
Gregor Mendel
(http://www.newworldencyclopedia.org/entry/Gregor_Mendel,
accessed 6 March 2012)
Sometimes alleles aren’t recessive or dominant instead they
are of incomplete dominance. This is
stated as heterozygous genotype results in a phenotype that is halfway between
the two homozygous phenotypes. This
creates a phenomenon of whether a person has the trait of curly, straight, or
wavy hair.
Co-dominance is when both alleles are expressed the
same. An example of co-dominance is
sickle cell anemia where hemoglobin in red blood cells crystalize in lower
oxygen levels. In result the red blood
cells have a crescent shape and are delicate.
In sickle cell anemia the odd shaped red blood cells clog blood vessels
restricting oxygenated blood flow. This
is due to one of two alleles involved in hemoglobin making in red blood
cells. People homozygous for sickle cell
anemia rarely live into their thirties.
Heterozygous people who carry the trait have equal amounts of each type
of hemoglobin. These people might feel
some minor effects but usually do not.
Other Factors Influence Inheritance Patterns and
Phenotype
Only three genes control a person’s eye color. Many traits are not due to one pair of genes
but many genes act together at the same time called polygenic inheritance. An example of polygenic inheritance is a
person’s height, body size, and shape.
The combination of alleles determines whether or not a person will be
tall, short, big, small, ect. Other
conditions influenced by polygenic inheritance researchers are starting to
understand including cancer and heart disease.
Environmental influences and our genotype are determined by
phenotype. People in developed countries
tend to be larger than people in less developed countries. This has happened in too short of time for
genetics to only contribute to people getting larger so quick. Environmental impact also contributes to
people getting larger quickly, affecting the gene pool. People’s actions and the risks they take with
their health play a huge part in whether a disease will actually develop. Knowing your family history is important to
be aware of because a person can better protect themselves by their
actions. Huntington’s disease is the
exception to this and is always fatal.
Many alleles are inherited together because they are joined
on the same chromosome. These alleles
are called linked alleles. During the reshuffling
of alleles across each pair of autosomes during meiosis sometimes linked
alleles are not inherited together.
Genetic variability is a result of the assortment of alleles on
different chromosomes, shuffling are of linked alleles crossing over between
autosomes, and the random fertilization of an egg by sperm.
Sex-linked Inheritance: X and Y Chromosomes Carry
Different Genes
Chromosomes can be identified in cells only just before cell
division. This exhibits all the
chromosomes of an organism called a karyotype.
A human karyotype has 22 matching chromosomes and one pair of sex
chromosomes.
Karyotype
(http://www.ds-health.com/trisomy.htm,
accessed 26 Feb 2012) The mother/woman has two X chromosomes in which one X is
donated to her offspring. The father has
one X chromosome and one Y chromosome in which one is donated to
offspring. If the father donates a Y
chromosome the baby will be a boy and if an X chromosome is donated then the
baby will be a girl.
The father determines the sex of all fertilized eggs. Women have a double X sex chromosome that is
a homologous pair. Males don’t have this
because they contain an X and Y causing a greater risk for diseases associated
with the recessive alleles on the male’s sex chromosome. The inheritance patterns on genes located on
sex chromosomes is called sex-linked inheritance. Genes on the Y chromosome influence
differences in male organs, production of sperm, and the development of
secondary sex -characteristics. Where in
the females X chromosome genes act like paired genes. Hemophilia is a sex-linked inheritance from
the X chromosome. Hemophilia is better
known as “bleeder’s disease” and is a lack in blood clotting. This disease
is more common in males than females because females inherit one normal allele
so she remains a disease carrier. If the
father is a carrier only his daughters will be carriers. If the mother is a carrier then all her sons
will be carriers. Almost all X linked
diseases are caused by recessive alleles not dominant alleles.
Some non sex genes in the 22 remaining chromosomes influence
different traits. For instance the allele that causes baldness can be in both
men and women. The baldness allele is
recessive in women but men become bald even when baldness is heterozygous. The difference between men and women has to
do with testosterone. Influences by genes
on sex chromosomes can convert recessive genes into dominant genes.
Chromosomes May be Altered in Number or Structure
Most embryos die before anyone is aware of them if they have
errors or missing chromosomes. Failure
of homologous chromosomes or sister chromatids to split correctly is called
nondisjunction. During meiosis when
sister chromatids don’t separate correctly the result is a change in the
chromosome number of sperm or egg cells.
The mishaps during meiosis are very detrimental because they can alter
the development of the entire being. If
a mishap happens during mitosis then the two daughter cells usually die and new
cells replace the two damaged ones. Problems
that happen during mitosis aren’t nearly as serious as problems that occur
during meiosis.
Sometimes chromosome number alterations don’t make the
embryo die. Some babies are born with
altered chromosomal numbers. The most
common chromosome number alterations are Down syndrome. The most common type of Down syndrome is when
the baby is born with three copies of chromosome number 21. One in 1,000babies is born with Down
syndrome.
(http://www.ds-health.com/trisomy.htm,
accessed 26 Feb 2012)
The likelihood of a
baby born with Down syndrome increases with how old the mother is when the baby
is born. Mothers under the age of thirty
have a one and 1,300 chance of having a baby with Down syndrome where mothers
who are forty have a one in 100 chance.
Then when mothers are 45 the probability of having a baby with Down
syndrome rises to one in 25. There is a
test called an amniocentesis where amniotic fluid is tested to detect any
chromosomal abnormalities.
Alterations in sex chromosomes can also produce different
syndromes. In Jacob syndrome a male has
one X and two Y chromosomes. The men
with this syndrome tend to be tall and can have some mental impairment.
Kline Felter syndrome
( http://images.search.yahoo.com/images/,
accessed Feb 27 2012) Kline Felter
syndrome is males having two X and one Y chromosomes. They are also usually tall and have mild
mental impairment. They are sterile and
may develop breasts because of the extra X chromosome. The syndrome called Trisomy-X means a woman
has three X chromosomes. Women who have
this syndrome usually have no effects except for the possibility of mild
retardation.
(http://babylab8.wikispaces.com/TURNER%27S+SYNDROME-EH,
accessed 27 Feb 2012)
Turner syndrome is
rare because usually the embryo aborts before the baby is born. People with this syndrome are female and only
have one X chromosome. They are sterile
and their bodies look childlike but besides that there aren’t any mental
problems.
There are other chromosomal problems can occur besides extra
chromosomes. In deletion, a piece of a
chromosome breaks off and is lost. When deletion happens the egg, sperm or embryo
all die. Babies that are born without a
specific chromosome result in mental and physical retardation. Sometimes a piece of a chromosome breaks off
but reattaches on a different place either on that chromosome or a different
chromosome called translocation. Even
though all the genes are still present the order isn’t correct. This results in slight changes in gene
expression like the increased chance of certain cancers.
Many Inherited Genetic Disorders Involve Recessive
Alleles
The expression of inherits genetic disorders only happen if
a person inherits two defective alleles.
If a parent is the carrier of a defective allele but has one correct
allele then that parent will remain only a carrier. The parent has the possibility of passing
defective alleles to their children. Sometimes
more than one gene pair causes a disease.
Enzyme deficiencies are caused by a specific gene on a chromosome. The combination creates sometimes rare and
deadly diseases. Tests are available to
determine anyone who is a carrier of these diseases. The most well-known of these diseases is Huntington’s
disease. Huntington’s affects people who
carry this dominant allele. They show
symptoms in their 30’s and are usually dead by the time they are 50. It’s a very cruel disease that causes a lot
of suffering. There is genetic testing
for Huntington’s and other inherited disorders.
Scientists are working intensely to identify all 22,000 genes
responsible for increasing the chances of breast cancer, skin cancer, and
osteoporosis. Preventing and treating
these genetic diseases is greatly researched, especially with new technology
being invented.
Genes Code for Proteins, not for Specific Behaviors
To become a human being a specific set of instructions have
to be precisely carried out. Genes
represent the set of instructions needed and can determine a person’s unique
physical traits. Genes code for specific
proteins that give a person curly, hair or different mood tendencies. Genes can’t be blamed for the bad or good
things people do. Proteins make up many
structures within cells and control a cells function. Together genes and their proteins can
influence a person’s mood and other tendencies.
But there isn’t any evidence that a specific gene causes happiness or
depression.
Chapter 20
DNA Sequencing Reveals Structure of DNA
Biotechnology is biological knowledge that is used for human
purposes. Recombinant DNA is defined as
genetically engineered DNA prepared by transplanting or splicing genes from one
species into the cells of a host organism of a different species. Such DNA
becomes part of the host's genetic makeup and is replicated (http://www.answers.com/topic/recombinant-dna,
accessed 9 March 2012). Genetic
engineering is the manipulation of the genetic makeup of cells or an entire
organism. Genetic engineering holds a
lot of promise for the future but is still very new. Determining the precise sequence
of base pairs that make up the individual DNA strands can be done. First scientists put millions of identical
copies of a single strand of DNA to be sequenced in a test tube. Then short strands DNA called primers are
added, whose job is to bind to each one of the ends of the DNA. It is the starting point of DNA and
synthesizes a new complimentary DNA strand.
Next the nucleotides are put in the mix and an enzyme is added called
DNA polymerase that helps the nucleotides to create the growing strand. Synthesis of DNA has then begun. Using a process called gel electrophoresis;
an electrical field causes the DNA pieces to navigate through the gel. (This is done on a flat surface) The single strand sequence of DNA is
complimentary to the original DNA fragments.
DNA can be cloned in the Laboratory
Recombinant DNA is a different process when dealing with
plants and animals. With the ability to
recombine DNA has the ability for scientists to create organisms that have
never been created before. Recombinant
DNA also has the ability to fix defective human genes. Recombinant DNA technology is the process of
cutting, slicing, and copying DNA and the genes it holds. Recombinant DNA technology needs special
components and tools including restrictive enzymes are enzymes that naturally
occur in some bacterias. This is done by
breaking the bonds between the base pairs in DNA. In nature these enzymes cut up any raiding
viruses. The most useful cut is in a
palindromic DNA sequence leaving two complimentary short, single strands of DNA
that are complimentary to any other DNA containing the same enzyme. DNA ligases are enzymes that bind DNA
fragments back together after a restricting enzyme has cut them apart. Plasmids are important and are self-replicating
DNA molecules that are found in bacteria.
Plasmids are round and small.
They aren’t a natural part of bacterial chromosomes but are very
important in non-normal gene replication done in labs.
The technique for producing cloned genes with recombinant
DNA includes 1. Isolating DNA plasmids and the human DNA of interest 2. Cutting
both DNA’s with the same restricting enzyme 3. Mixing the DNA fragments with
the cut plasmids 4. Add DNA ligase to
complete the connections 5. Introducing the new plasmids into bacteria 6.
Select the bacteria containing the gene of interest and allowing them to
reproduce. This technique can create
endless amounts of a precise protein.
Another way to clone DNA is through polymerase chain
reaction. This technique is fast using
small pieces of DNA and makes millions of copies of the DNA. This is done by heating the piece of DNA to
unwind it. Then they are mixed with
complimentary primers. Next nucleotides
are added that are important in creating new DNA strands. Lastly DNA polymerase is added creating the
enzyme to catalyze and attach the nucleotides to the growing DNA strands. Heating and cooling set the strands and after
20 times there is over a million identical DNA copies (clones).
(http://images.search.yahoo.com/image,
accessed 10 March 2012)
Sometimes DNA needs to be identified when someone doesn’t
know where it came from. This technique
is used mostly at crime scenes. It is
used to figure out who an unknown deceased person’s identity is, who the father
of a baby is, and to trace someone’s ancestry.
This technique allows someone to identify the source of DNA after it has
been adequately copied by the polymerase chain reaction. Then restriction enzymes are used to cut the DNA
into pieces. Next he DNA is places in
gel that separates them according to size.
A printout of DNA fragments on the gel is called electropherogram or DNA
fingerprint.
Genetic Engineering Creates Transgenic Organisms
Genetic engineering is the ability to produce transgenic organisms
that can transfer one or more different species of genes to create many new
possibilities. There are many uses for
transgenic bacteria. They help to produce or replace hormones in
the body that aren’t being produced with proteins. When a person is missing a certain hormone it
can be life threatening. One instance of
this is insulin and if the body doesn’t produce it and the hormone isn’t being
replaced the person won’t survive. There
are also non hormones that are created such as tissue plasminogen activator
that prevents or reverses blood clots.
Another use for transgenic bacteria is the production of vaccines. I learned that vaccines are usually made from
dead or weak organisms that actually cause the disease. I also learned that sometimes vaccines can
actually give you the disease they are trying to protect you from. The reason why some vaccines are expensive or
limited is because the organisms that cause a disease evolve. Sometimes vaccines have to be reworked
yearly. Lots of time is spent trying to
make successful vaccines. Other uses
that are cleaning up toxic waste and oil pollutants, removing sulfur from coal,
making citric acid, and making ethanol.
Transgenic plants aren’t as easy to make but hold a lot of
promise. One way of changing plants DNA
is by shooting recombinant DNA into plant cells at high velocity. Another way is by shocking plants at high
voltage in the presence of recombinant DNA or by putting infected bacterium
with DNA that then infects the plant.
Some plants then may incorporate the new DNA into the original plant DNA
creating new traits in the plant. One
plant that genetic engineering has been so successful with is tomatoes. Tomato plants can now resist freezing, have a
longer shelf life, and resists pests. Other
benefits of genetic engineering are larger leaves to aid in photosynthesis,
better roots to fight drought, and plants that mature earlier to yield more
food. One thing I found disturbing was
the information on edible vaccines. They
have made a Hepatitis B vaccine produced in raw potatoes and are working on
many vaccines to be produced in bananas.
In some ways I understand especially for third world countries but I
question if this is truly safe without any side effects.
(http://images.search.yahoo.com/images,
accessed 9 March 2012)
Even harder to produce than transgenic plants is transgenic
animals. This is because the numbers of
eggs available are limited and only 10% of eggs combine recombinant DNA on
their own. The process begins with
inserting DNA into already fertilized eggs.
Even though there are some difficulties with transgenic animals new
advances are happening. One way is with
growth hormone, one in particular is
Bovine growth hormone that makes animals grow faster and larger which
some people are uneasy about.
Gene Therapy: The Hope of the Future?
Gene therapy is when human genes are inserted into human
cells to treat or correct a disease.
There have already been exact gene mutations found on specific
chromosomes that cause many genetic problems.
Researchers hope that in the future these problems could be fixed with
gene therapy. One problem is that in
adults some genes have already mutated through the DNA replication
process. Replacing a missing gene might
seem difficult but is being researched.
Also the question is if the offspring of a person who received gene
therapy would still inherit the mutation.
It isn’t necessary to replace a missing gene into all the
cells. Rather if an adequate number of
new genes were replaced so enough of the missing protein was produced
preventing the disease. One way of doing
this is through vectors (transporters) that deliver genes into cells. The best vectors are viruses called
retroviruses. The retroviruses splice
their own RNA based genetic code permanently into the DNA they infect. Another way is by taking tissue from the body
and exposing it to the retrovirus then returning it to the body. Researchers then hope the cells will then
integrate the genes back to where the tissue was taken from. There are some drawbacks to retroviruses and
many techniques are still very experimental.
There are successful gene therapy stories and treatment is
helping people. Some people with
conditions that have immune system deficiencies are susceptible to
infections. But now with gene therapy
treatment people can live better lives.
Cancer may also be treated with gene therapy soon. There are many different approaches being researched
and tested to treat cancers. The future
will hold many new breakthroughs in our lifetime.
